This invention relates to wireless communications and more particularly to a system for dynamic adaptation of data/channel coding.
Transmission of digitally encoded speech over wireless channels in a cellular environment usually requires the use of error control techniques to combat the noisy nature of such channels. In cellular applications, however, the characteristics of the channel are highly non-stationary, that is, periods of relatively error-free signal alternate with periods of strongly deteriorated signal. The traditional solution to this problem is to allocate to error detection and correction enough bandwidth to deal with the xe2x80x9caverage channelxe2x80x9d, sacrificing optimality for the two extreme cases of good and bad channels.
This static approach is clearly not optimal: in good channel conditions most of the resources employed by error control are redundant, and could be better used to increase the speech quality, while in bad channels, error control should be reinforced by using resources made available by a lower bit rate speech codec. Moreover, the cellular channel is quite bipolar, that is, oscillates in time between good and bad channels, passing only a fraction of the time of a call in the xe2x80x9caverage channelxe2x80x9d condition for which the static solution was designed. Unequal Error Protection is used in most cellular standards. In Unequal Error Protection, speech bits are divided into classes of decreasing perceptual importance and each class is encoded with appropriate rates of protection including no protection. Although the Unequal Error Protection approach used in most cellular standards somewhat mitigates the flaw of using the xe2x80x9caverage channelxe2x80x9d approach, a better solution is desirable.
In accordance with one embodiment of the present invention, a system is presented that allows one station to communicate with a second station. The station monitors the quality of the channels connecting them and adapts their data and error control rates accordingly.